Dense Molecular Gas in the Starburst Nucleus of NGC 1808

作者：Salak Dragan^*; Tomiyasu Yuto; Nakai Naomasa; Kuno Nario; Miyamoto Yusuke; Kaneko Hiroyuki

来源：Astrophysical Journal, 2018, 856(2): 97.

DOI：10.3847/1538-4357/aab2ac

• galaxies: individual (NGC 1808)
• galaxies: ISM
• galaxies: nuclei
• galaxies: starburst
• ISM: structure

Dense molecular gas tracers in the central 1 kpc region of the superwind galaxy NGC 1808 have been imaged by ALMA at a resolution of 1 '' (similar to 50 pc). Integrated intensities and line intensity ratios of HCN (1-0), (HCN)-C-13 (1-0), HCO+ (1-0), (HCO+)-C-13 (1-0), HOC+ (1-0), HCO+ (4-3), CS (2-1), C2H (1-0), and previously detected CO (1-0) and CO (3-2) are presented. SiO (2-1) and HNCO (4-3) are detected toward the circumnuclear disk (CND), indicating the presence of shocked dense gas. There is evidence that an enhanced intensity ratio of HCN (1-0)/HCO+ (1-0) reflects star formation activity, possibly in terms of shock heating and electron excitation in the CND and a star-forming ring at radius similar to 300 pc. A non-local thermodynamic equilibrium analysis indicates that the molecular gas traced by HCN, (HCN)-C-13, HCO+, and (HCO+)-C-13 in the CND is dense (n(H2) similar to 10(5) cm(-3)) and warm (20 K less than or similar to T-k less than or similar to 100 K). The calculations yield a low average gas density of n(H2) similar to 10(2)-10(3) cm(-3) for a temperature of T-k greater than or similar to 30 K in the nuclear outflow. Dense gas tracers HCN (1-0), HCO+ (1-0), CS (2-1), and C2H (1-0) are detected for the first time in the superwind of NGC 1808, confirming the presence of a velocity gradient in the outflow direction.

• 出版日期2018-4-1
• 单位中国科学院国家天文台